Electrical power for an integrated circuit (IC), such as but not limited to a microprocessor chip of a personal computer, is typically supplied by one or more direct current (battery) power sources, such as a buck-mode, pulse width modulation (PWM) based, DC-DC converter of the type diagrammatically shown in FIG. 1. As shown therein, a PWM control circuit 1 supplies a synchronous PWM signal to a switching circuit driver 2, that controls the turn-on and turn-off of a pair of electronic power switching devices, to which a powered load 9 is coupled. In the illustrated DC-DC converter, the electronic power switching devices comprise an upper (or high side) power NMOSFET (or NFET) device 3, and a lower (or low side) power NFET device 4, having their drain-source current flow paths connected in series between a pair of power supply rails (e.g., VIN and ground (GND)).
The upper NFET device UFET 3 is turned on and off by an upper gate-switching signal UGATE applied to its gate from driver 2, while the lower NFET device LFET 4 is turned on and off by a lower gate-switching signal LGATE supplied from driver 2. A common or phase node 5 between the two NFETs is coupled through an inductor 6 to a load reservoir capacitor 7 that is coupled to a reference voltage terminal (GND). The connection 8 between inductor 6 and capacitor 7 serves as an output node from which a desired (regulated) DC output voltage Vout is applied to a LOAD 9 (coupled to GND).
The output node connection 8 is also fed back via a feedback resistor 12 to error amplifier circuitry within the PWM controller 1. The error amplifier circuitry is used to regulate the converter's DC output voltage relative to a reference voltage supply. In addition, the common node 5 between the controllably switched NFETs is coupled via a current sense resistor 11 to current-sensing circuitry within the controller 1, in response to which the controller adjusts duty ratio of the PWM signal, as necessary, to maintain the converter's DC output within a prescribed set of parameters.
In the course of supplying power from the power supply to its powered components, it is of critical importance that an anomaly in the power supply path, such as a short circuit in the upper switched NFET (which may be due to a bad component or inadvertent shorting of its drain and during manufacture), not propagate to downstream circuitry, especially a microprocessor chip.